Diffractive optical element with integrated in-coupling, exit pupil expansion, and out-coupling

ABSTRACT

In an optical near eye display system, a monolithic three-dimensional optical microstructure is formed by a waveguide substrate with at least one DOE having grating regions that integrate the functions of in-coupling of incident light into the waveguide, exit pupil expansion in one or two directions, and out-coupling of light from the waveguide within a single optical element. An in-coupling region of the DOE couples the incident light into the waveguide and to a beam steering and out-coupling region. The beam steering and out-coupling region provides exit pupil expansion and couples light out of the waveguide. The beam steering and out-coupling region of the DOE can be configured with a two-dimensional (2D) grating that is periodic in two directions.

BACKGROUND

Diffractive optical elements (DOEs) are optical elements with a periodicstructure that are commonly utilized in applications ranging frombio-technology, material processing, sensing, and testing to technicaloptics and optical metrology. By incorporating DOEs in an optical fieldof a laser or emissive display, for example, the light's “shape” can becontrolled and changed flexibly according to application needs.

SUMMARY

In an optical near eye display system, a monolithic three-dimensionaloptical microstructure is formed by a waveguide substrate with at leastone DOE having grating regions that integrate the functions ofin-coupling of incident light into the waveguide, exit pupil expansionin one or two directions, and out-coupling of light from the waveguidewithin a single optical element. An in-coupling region of the DOEcouples the incident light into the waveguide and to a beam steering andout-coupling region of the DOE. The beam steering and out-couplingregion provides exit pupil expansion and couples light out of thewaveguide. The beam steering and out-coupling region of the DOE can beconfigured with a two-dimensional (2D) grating that is periodic in twodirections. The 2D grating provides multiple optical paths to a givenpoint in the beam steering and out-coupling region of the DOE in whichthe differences in the optical path lengths are larger than thecoherence length. As a result, optical interference is reduced in thedisplay system and display uniformity and optical resolution isincreased.

Optical interference is typically manifested as dark stripes in thedisplay which is referred to as “banding.” Banding may be morepronounced when polymeric materials are used in volume production of theDOE to minimize system weight as polymeric materials may have lessoptimal optical properties compared with other materials such as glass.Furthermore, by integrating the in-coupling, exit pupil expansion, andout-coupling functions into a single monolithic optical microstructureof the DOE, discontinuities at boundaries between gratings areeliminated which may further increase optical resolution in the near eyedisplay system. In addition, the integrated DOE can reduce overallcomponent count and weight which can be desirable in applications suchas head mounted display (HMD).

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter. Furthermore, the claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in any part ofthis disclosure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an illustrative near eye display systemwhich may incorporate a diffractive optical element (DOE) withintegrated in-coupling, pupil expansion, and out-coupling;

FIG. 2 shows propagation of light in a waveguide by total internalreflection;

FIG. 3 shows a view of an illustrative exit pupil expander;

FIG. 4 shows a view of the illustrative exit pupil expander in which theexit pupil is expanded along two directions;

FIG. 5 shows an illustrative arrangement of three discrete DOEs;

FIG. 6 shows an illustrative example of a monolithic DOE with integratedin-coupling, pupil expansion, and out-coupling;

FIGS. 7-10 show various illustrative two-dimensional (2D) gratings;

FIG. 11 shows an illustrative arrangement for DOE fabrication using amask that moves relative to a substrate;

FIG. 12 shows an illustrative method;

FIG. 13 is a pictorial view of an illustrative example of a virtualreality or mixed reality head mounted display (HMD) device;

FIG. 14 shows a block diagram of an illustrative example of a virtualreality or mixed reality HMD device; and

FIG. 15 shows a block diagram of an illustrative electronic device thatincorporates an exit pupil expander.

Like reference numerals indicate like elements in the drawings. Elementsare not drawn to scale unless otherwise indicated.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of an illustrative optical near eye displaysystem 100 which may incorporate one or more diffractive opticalelements (DOEs) with integrated in-coupling, exit pupil expansion in oneor two directions, and out-coupling using a monolithic waveguidesubstrate. Near eye display systems are frequently used, for example, inhead mounted display (HMD) devices in industrial, commercial, andconsumer applications. Other devices and systems may also use DOEs withintegrated in-coupling, exit pupil expansion in one or two directions,and out-coupling, as described below. The near eye display system 100 isintended to be an example that is used to illustrate various featuresand aspects, and the present DOEs are not necessarily limited to neareye display systems.

System 100 may include an imager 105 that works with an optical system110 to deliver images as a virtual display to a user's eye 115. Theimager 105 may include, for example, RGB (red, green, blue) lightemitting diodes (LEDs), LCOS (liquid crystal on silicon) devices, OLED(organic light emitting diode) arrays, MEMS (micro-electro mechanicalsystem) devices, or any other suitable displays or micro-displaysoperating in transmission, reflection, or emission. The imager 105 mayalso include mirrors and other components that enable a virtual displayto be composed and provide one or more input optical beams to theoptical system. The optical system 110 can typically include magnifyingoptics 120, pupil forming optics 125, and one or more waveguides 130.

In a near eye display system the imager does not actually shine theimages on a surface such as a glass lens to create the visual displayfor the user. This is not feasible because the human eye cannot focus onsomething that is that close. Indeed, rather than create a visible imageon a surface, the near eye optical system 100 uses the pupil formingoptics 125 to form a pupil and the eye 115 acts as the last element inthe optical chain and converts the light from the pupil into an image onthe eye's retina as a virtual display.

The waveguide 130 facilitates light transmission between the imager andthe eye. One or more waveguides can be utilized in the near eye displaysystem because they are transparent and because they are generally smalland lightweight (which is desirable in applications such as HMD deviceswhere size and weight is generally sought to be minimized for reasons ofperformance and user comfort). For example, the waveguide 130 can enablethe imager 105 to be located out of the way, for example, on the side ofthe head, leaving only a relatively small, light, and transparentwaveguide optical element in front of the eyes. In one implementation,the waveguide 130 operates using a principle of total internalreflection, as shown in FIG. 2, so that light can be coupled among thevarious optical elements in the system 100.

FIG. 3 shows a view of an illustrative exit pupil expander (EPE) 305.EPE 305 receives an input optical beam from the imager 105 throughmagnifying optics 120 to produce one or more output optical beams withexpanded exit pupil in one or two directions relative to the exit pupilof the imager (in general, the input may include more than one opticalbeam which may be produced by separate sources). The expanded exit pupiltypically facilitates a virtual display to be sufficiently sized to meetthe various design requirements of a given optical system, such as imageresolution, field of view, and the like, while enabling the imager andassociated components to be relatively light and compact.

The EPE 305 is configured, in this illustrative example, to supportbinocular operation for both the left and right eyes. Components thatmay be utilized for stereoscopic operation such as scanning mirrors,lenses, filters, beam splitters, MEMS devices, or the like are not shownin FIG. 3 for sake of clarity in exposition. The EPE 305 utilizes twoout-coupling gratings, 310 _(L) and 310 _(R) that are supported on awaveguide 330 and a central in-coupling grating 340. The in-coupling andout-coupling gratings may be configured using multiple DOEs, asdescribed in the illustrative example below. While the EPE 305 isdepicted as having a planar configuration, other shapes may also beutilized including, for example, curved or partially spherical shapes,in which case the gratings disposed thereon are non-co-planar.

As shown in FIG. 4, the EPE 305 may be configured to provide an expandedexit pupil in two directions (i.e., along each of a first and secondcoordinate axis). As shown, the exit pupil is expanded in both thevertical and horizontal directions. It may be understood that the terms“direction,” “horizontal,” and “vertical” are used primarily toestablish relative orientations in the illustrative examples shown anddescribed herein for ease of description. These terms may be intuitivefor a usage scenario in which the user of the near eye display device isupright and forward facing, but less intuitive for other usagescenarios. The listed terms are not to be construed to limit the scopeof the configurations (and usage scenarios therein) of DOEs withintegrated in-coupling, pupil expansion, and out-coupling.

FIG. 5 shows an illustrative arrangement 500 of three discrete DOEs thatmay be used as part of a waveguide to provide in-coupling and expansionof the exit pupil in two directions. In this illustrative example, eachDOE is an optical element comprising a periodic structure that canmodulate various properties of light in a one-dimensional (1D) periodicpattern such as the direction of optical axis, optical path length, andthe like. The first DOE, DOE 1 (indicated by reference numeral 505), isconfigured to couple the beam from the imager into the waveguide. Thesecond DOE, DOE 2 (510), expands the exit pupil in a first directionalong a first coordinate axis, and the third DOE, DOE 3 (515), expandsthe exit pupil in a second direction along a second coordinate axis andcouples light out of the waveguide. The angle η is a rotation anglebetween the periodic lines of DOE 2 and DOE 3 as shown. DOE 1 thusfunctions as an in-coupling grating and DOE 3 functions as anout-coupling grating while expanding the pupil in one direction. DOE 2may be viewed as an intermediate grating that functions to couple lightbetween the in-coupling and out-coupling gratings while performing exitpupil expansion in the other direction. Using such intermediate gratingmay eliminate a need for conventional functionalities for exit pupilexpansion in an EPE such as collimating lenses.

Some near eye display system applications, such as those using HMDdevices for example, can benefit by minimization of weight and bulk. Asa result, the DOEs and waveguides used in an EPE may be fabricated usinglightweight polymers. Such polymeric components can support design goalsfor size, weight, and cost, and generally facilitate manufacturability,particularly in volume production settings. However, polymeric opticalelements generally have lower optical resolution relative to heavierhigh quality glass. Such reduced optical resolution and the waveguide'sconfiguration to be relatively thin for weight savings and packagingconstraints within a device can result in optical interference thatappears as a phenomenon referred to as “banding” in the display. Theoptical interference that results in banding arises from lightpropagating within the EPE that has several paths to the same location,in which the optical path lengths differ.

The banding is generally visible in the form of dark stripes whichdecrease optical uniformity of the display. Their location on thedisplay may depend on small nanometer-scale variations in the opticalelements including the DOEs in one or more of thickness, surfaceroughness, or grating geometry including grating line width, angle, fillfactor, or the like. Such variation can be difficult to characterize andmanage using tools that are generally available in manufacturingenvironments, and particularly for volume production. Conventionalsolutions to reduce banding include using thicker waveguides which canadd weight and complicate package design for devices and systems. Othersolutions use pupil expansion in the EPE in just one direction which canresult in a narrow viewing angle and heightened sensitivity to naturaleye variations among users.

The arrows in FIG. 5 show light propagating in DOE 2 when configured asa 1D grating that is periodic in one direction. As shown, lightpropagates from left to right in the waveguide and propagates downwardsthrough refraction. As a result, light can loop around to any givenpoint within DOE 2 over several paths in which the length of each pathis essentially the same. However, since the differences in optical pathlengths are smaller than the coherence length (i.e., a propagationdistance over which the light may be considered coherent), even smalldifferences in path length can result in strong interference in DOE 3and reduce optical resolution, uniformity, and color balance in theoptical display system. Use of a 1D grating for DOE 2 may alsonecessitate tight manufacturing tolerances to help reduce variabilityand achieve a target optical resolution. Maintaining tight manufacturingtolerances can be expensive and problematic, particularly for volumeproduction of DOEs in the optical near eye display systems. Furthermore,the discontinuities presented by the boundaries between DOEs 1, 2, and 3can typically cause undesired refraction which reduces opticalresolution. In some implementations, the out-coupling DOE 3 may beapodized with shallow gratings in order to minimize the loss in opticalresolution from the boundary with the upstream DOE.

By comparison to the DOE arrangement 500 using three discrete DOEs with1D gratings shown in FIG. 5, FIG. 6 shows light propagation in a DOE 605used in an EPE that integrates the functions of in-coupling of incidentlight, exit pupil expansion in one or two directions, and out-couplinglight out of the EPE waveguide using a single monolithic opticalstructure. The term “monolithic” as used here refers to a unitarywaveguide substrate without boundaries between the diffraction gratingsthat are formed thereon. For example, the waveguide substrate may beformed using a single piece of optical glass, polymer, or other suitablematerial and can include one or more DOEs that provide integratedoptical functions.

An in-coupling region 610 of the DOE 605 couples incident light into thewaveguide and to a downstream beam steering and out-coupling region 615which couples light out of the waveguide with an expanded exit pupil inone or two directions compared to the incident light. The in-couplingregion 610 may be configured as either a 1D grating, or as a 2D gratingthat is periodic in two directions. Such 2D gratings may be referred toas “crossed gratings” and the two directions may be, but are notnecessarily, perpendicular.

In this illustrative example, the beam steering and out-coupling region615 of the integrated DOE 605 is configured as 2D grating that isperiodic in two directions. In this illustrative example as shown inFIG. 6, light propagates both up and to the right (in a “right path”),and down and to the left (in a “left path”), as representativelyindicated by reference numerals 625 and 630 in FIG. 6. Light can arriveat a given point in the beam steering and out-coupling region 615 bylooping along both the left paths and right paths. Unlike a 1D grating,the optical path lengths in the 2D grating in the beam steering andout-coupling region 615 are different for the different paths, and thedifferences in optical path lengths are larger than the coherencelength. Optical interference is therefore minimized and opticalresolution, uniformity, and color balance is increased in the displaysystem as compared to the 1D grating configuration shown in FIG. 5. Inaddition, optical resolution is typically further increased in theintegrated DOE 605 by reducing the undesired diffraction that wouldotherwise occur at the boundaries between discrete DOEs (e.g., DOEs 1,2, and 3 in FIG. 5).

In this particular illustrative example, the beam steering andout-coupling region 615 of the DOE 605 is configured to simultaneouslyexpand the exit pupil in two directions. However, in alternativeimplementations, the beam steering and out-coupling region may expandthe exit pupil in one direction and an additional optical element orgrating may perform exit pupil expansion in a second direction. Suchadditional element may be included as an integrated element within themonolithic structure of the waveguide in some implementations, or beembodied as a separate discrete component in the optical near eyedisplay system in other implementations.

The 2D gratings for the in-coupling region 610 and the beam steering andout-coupling region 615 of the DOE 605 may utilize a variety ofstructures that are periodic in two directions according to the needs ofa particular implementation. For example, FIGS. 7, 8, 9, and 10 depictvarious illustrative 2D gratings as respectively indicated by referencenumerals 705, 805, 905, and 1005. The 2D gratings in the drawings areillustrative and not limiting, and it is contemplated that variationsfrom the 2D gratings shown may also be utilized. Gratings may includesymmetric and/or asymmetric features including slanted gratings (i.e.,gratings having walls that are non-orthogonal according to one or morepredetermined angles to a plane of the waveguide) and blazed gratings(i.e., gratings having asymmetric triangular or sawtooth profiles) insome cases. Various suitable surface relief contours, filling factors,grating periods, and grating dimensions can also be utilized accordingto the needs of a particular implementation.

FIG. 7 shows a 2D grating 705 that includes quadrangular elements thatproject from a substrate. The quadrangular elements can also beconfigured to be asymmetric such as being slanted or blazed.Non-quadrangular three-dimensional geometries (both symmetric andasymmetric) may also be utilized for a 2D grating including, forexample, cylindrical elements, polygonal elements, elliptical elements,or the like. For example, FIG. 8 shows a 2D grating 805 that includespyramidal elements, and FIG. 9 shows a 2D grating 905 that includeselements that have a blazed profile in each of the x and z directions.Gratings may also have elements with curved profiles, as shown in theillustrative 2D grating 1005 in FIG. 10.

FIG. 11 shows an illustrative arrangement for DOE fabrication using amask 1105 that moves relative to a photosensitive grating substrate 1110within an enclosure 1115. A reactive ion etching plasma 1120 is used toadjust the thickness of the etching on the grating substrate at variouspositions by moving the substrate relative to the mask using, forexample, a computer-controller stepper functionality or other suitablecontrol system. In an illustrative example, the etching may be performedusing a reactive ion beam etching (RIBE). However, other variations ofion beam etching may be utilized in various implementations including,for example, magnetron reactive ion etching (MRIE), high density plasmaetching (HDP), transformer coupled plasma etching (TCP), inductivelycoupled plasma etching (ICP), and electron cyclotron resonance plasmaetching (ECR).

Multi-beam interference holography may be used in some implementationsto produce the two-direction periodic three-dimensional microstructuresin a 2D grating in a DOE. In some manufacturing scenarios, multipleexposures may be utilized in which the substrate is rotated, for exampleby 90 degrees, between exposures.

FIG. 12 is a flowchart of an illustrative method 1200. Unlessspecifically stated, the methods or steps shown in the flowchart anddescribed in the accompanying text are not constrained to a particularorder or sequence. In addition, some of the methods or steps thereof canoccur or be performed concurrently and not all the methods or steps haveto be performed in a given implementation depending on the requirementsof such implementation and some methods or steps may be optionallyutilized.

In step 1205, light is received at an in-coupling region of a DOE. TheDOE is configured as an EPE and integrates in-coupling, exit pupilexpansion in one or two directions, and out-coupling within a singlemonolithic optical element. In step 1210, the exit pupil of the receivedlight is expanded along a first coordinate axis using the beam steeringand out-coupling region of the DOE. In step 1215, the exit pupil isexpanded along a second coordinate axis. As noted above, the exit pupilexpansion in the second direction may be performed using another opticalelement or DOE (which can be integrated in the waveguide or beimplemented as a separate discrete element) in some alternativeimplementations. Accordingly, the in-coupling region of the DOE can beconfigured as either a 1D grating or as a 2D grating. The beam steeringand out-coupling region of the DOE is configured as a 2D grating. Instep 1220, light is output from the beam steering and out-couplingregion of the DOE with an expanded exit pupil relative to the receivedlight at the in-coupling region along the first and second coordinateaxes.

A DOE with integrated in-coupling, exit pupil expansion, andout-coupling may be incorporated into a display system that is utilizedin a virtual or mixed reality display device. Such device may take anysuitable form, including but not limited to near-eye devices such as anHMD device. A see-through display may be used in some implementationswhile an opaque (i.e., non-see-through) display using a camera-basedpass-through or outward facing sensor, for example, may be used in otherimplementations.

FIG. 13 shows one particular illustrative example of a see-through,mixed reality or virtual reality display system 1300, and FIG. 14 showsa functional block diagram of the system 1300. Display system 1300comprises one or more lenses 1302 that form a part of a see-throughdisplay subsystem 1304, such that images may be displayed using lenses1302 (e.g. using projection onto lenses 1302, one or more waveguidesystems incorporated into the lenses 1302, and/or in any other suitablemanner). Display system 1300 further comprises one or moreoutward-facing image sensors 1306 configured to acquire images of abackground scene and/or physical environment being viewed by a user, andmay include one or more microphones 1308 configured to detect sounds,such as voice commands from a user. Outward-facing image sensors 1306may include one or more depth sensors and/or one or more two-dimensionalimage sensors. In alternative arrangements, as noted above, a mixedreality or virtual reality display system, instead of incorporating asee-through display subsystem, may display mixed reality or virtualreality images through a viewfinder mode for an outward-facing imagesensor.

The display system 1300 may further include a gaze detection subsystem1310 configured for detecting a direction of gaze of each eye of a useror a direction or location of focus, as described above. Gaze detectionsubsystem 1310 may be configured to determine gaze directions of each ofa user's eyes in any suitable manner. For example, in the illustrativeexample shown, a gaze detection subsystem 1310 includes one or moreglint sources 1312, such as infrared light sources, that are configuredto cause a glint of light to reflect from each eyeball of a user, andone or more image sensors 1314, such as inward-facing sensors, that areconfigured to capture an image of each eyeball of the user. Changes inthe glints from the user's eyeballs and/or a location of a user's pupil,as determined from image data gathered using the image sensor(s) 1314,may be used to determine a direction of gaze.

In addition, a location at which gaze lines projected from the user'seyes intersect the external display may be used to determine an objectat which the user is gazing (e.g. a displayed virtual object and/or realbackground object). Gaze detection subsystem 1310 may have any suitablenumber and arrangement of light sources and image sensors. In someimplementations, the gaze detection subsystem 1310 may be omitted.

The display system 1300 may also include additional sensors. Forexample, display system 1300 may comprise a global positioning system(GPS) subsystem 1316 to allow a location of the display system 1300 tobe determined. This may help to identify real world objects, such asbuildings, etc. that may be located in the user's adjoining physicalenvironment.

The display system 1300 may further include one or more motion sensors1318 (e.g., inertial, multi-axis gyroscopic, or acceleration sensors) todetect movement and position/orientation/pose of a user's head when theuser is wearing the system as part of a mixed reality or virtual realityHMD device. Motion data may be used, potentially along with eye-trackingglint data and outward-facing image data, for gaze detection, as well asfor image stabilization to help correct for blur in images from theoutward-facing image sensor(s) 1306. The use of motion data may allowchanges in gaze location to be tracked even if image data fromoutward-facing image sensor(s) 1306 cannot be resolved.

In addition, motion sensors 1318, as well as microphone(s) 1308 and gazedetection subsystem 1310, also may be employed as user input devices,such that a user may interact with the display system 1300 via gesturesof the eye, neck and/or head, as well as via verbal commands in somecases. It may be understood that sensors illustrated in FIGS. 13 and 14and described in the accompanying text are included for the purpose ofexample and are not intended to be limiting in any manner, as any othersuitable sensors and/or combination of sensors may be utilized to meetthe needs of a particular implementation. For example, biometric sensors(e.g., for detecting heart and respiration rates, blood pressure, brainactivity, body temperature, etc.) or environmental sensors (e.g., fordetecting temperature, humidity, elevation, UV (ultraviolet) lightlevels, etc.) may be utilized in some implementations.

The display system 1300 can further include a controller 1320 having alogic subsystem 1322 and a data storage subsystem 1324 in communicationwith the sensors, gaze detection subsystem 1310, display subsystem 1304,and/or other components through a communications subsystem 1326. Thecommunications subsystem 1326 can also facilitate the display systembeing operated in conjunction with remotely located resources, such asprocessing, storage, power, data, and services. That is, in someimplementations, an HMD device can be operated as part of a system thatcan distribute resources and capabilities among different components andsubsystems.

The storage subsystem 1324 may include instructions stored thereon thatare executable by logic subsystem 1322, for example, to receive andinterpret inputs from the sensors, to identify location and movements ofa user, to identify real objects using surface reconstruction and othertechniques, and dim/fade the display based on distance to objects so asto enable the objects to be seen by the user, among other tasks.

The display system 1300 is configured with one or more audio transducers1328 (e.g., speakers, earphones, etc.) so that audio can be utilized aspart of a mixed reality or virtual reality experience. A powermanagement subsystem 1330 may include one or more batteries 1332 and/orprotection circuit modules (PCMs) and an associated charger interface1334 and/or remote power interface for supplying power to components inthe display system 1300.

It may be appreciated that the display system 1300 is described for thepurpose of example, and thus is not meant to be limiting. It is to befurther understood that the display device may include additional and/oralternative sensors, cameras, microphones, input devices, outputdevices, etc. than those shown without departing from the scope of thepresent arrangement. Additionally, the physical configuration of adisplay device and its various sensors and subcomponents may take avariety of different forms without departing from the scope of thepresent arrangement.

As shown in FIG. 15, an EPE incorporating a DOE with integratedin-coupling, exit pupil expansion, and out-coupling can be used in amobile or portable electronic device 1500, such as a mobile phone,smartphone, personal digital assistant (PDA), communicator, portableInternet appliance, hand-held computer, digital video or still camera,wearable computer, computer game device, specialized bring-to-the-eyeproduct for viewing, or other portable electronic device. As shown, theportable device 1500 includes a housing 1505 to house a communicationmodule 1510 for receiving and transmitting information from and to anexternal device, or a remote system or service (not shown).

The portable device 1500 may also include an image processing module1515 for handling the received and transmitted information, and avirtual display system 1520 to support viewing of images. The virtualdisplay system 1520 can include a micro-display or an imager 1525 and anoptical engine 1530. The image processing module 1515 may be operativelyconnected to the optical engine 1530 to provide image data, such asvideo data, to the imager 1525 to display an image thereon. An EPE 1535using a DOE with integrated in-coupling, exit pupil expansion, andout-coupling can be optically linked to an optical engine 1530.

An EPE using a DOE with integrated in-coupling, exit pupil expansion,and out-coupling may also be utilized in non-portable devices, such asgaming devices, multimedia consoles, personal computers, vendingmachines, smart appliances, Internet-connected devices, and homeappliances, such as an oven, microwave oven and other appliances, andother non-portable devices.

Various exemplary embodiments of the present diffractive optical elementwith integrated in-coupling, exit pupil expansion, and out-coupling arenow presented by way of illustration and not as an exhaustive list ofall embodiments. An example includes an optical element, comprising: asubstrate of optical material forming a waveguide; an in-coupling regionintegrated into the substrate, the in-coupling region having an inputsurface and configured to couple one or more optical beams incident onthe input surface into the waveguide; and a beam steering andout-coupling region integrated into the substrate and configured forpupil expansion of the one or more optical beams along a firstdirection, wherein the beam steering and out-coupling region isconfigured with a two-dimensional (2D) grating that is periodic in twodirections.

In another example, the 2D grating includes one of symmetric orasymmetric features. In another example, the asymmetric features includeone of slanted gratings or blazed gratings. In another example, the beamsteering and out-coupling region includes an output surface and isconfigured for pupil expansion of the one or more optical beams along asecond direction, and further configured to couple, as an output fromthe output surface, one or more optical beams with expanded pupilrelative to the input. In another example, differences among opticalpath lengths in the beam steering and out-coupling region exceed acoherence length so as to increase uniformity of the output opticalbeams.

A further examples includes an electronic device, comprising: a dataprocessing unit; an optical engine operatively connected to the dataprocessing unit for receiving image data from the data processing unit;an imager operatively connected to the optical engine to form imagesbased on the image data and to generate one or more input optical beamsincorporating the images; and an exit pupil expander, responsive to theone or more input optical beams, comprising a monolithic waveguidestructure on which multiple diffractive optical elements (DOEs) areintegrated, in which the exit pupil expander is configured to provideone or more output optical beams, using one or more of the DOEs, as anear eye virtual display with an expanded exit pupil, and wherein atleast one of the DOEs has a region configured to implement beam steeringand out-coupling of the output optical beams from the monolithicwaveguide structure.

In another example, at least one of the DOEs has a region configured toin-couple the input optical beams into the waveguide structure. Inanother example, the input optical beams received at the exit pupilexpander emanate as a virtual image produced by a micro-display orimager. In another example, the exit pupil expander provides pupilexpansion in two directions. In another example, the imager includes oneof light emitting diode, liquid crystal on silicon device, organic lightemitting diode array, or micro-electro mechanical system device. Inanother example, the imager comprises a micro-display operating in oneof transmission, reflection, or emission. In another example, theelectronic device is implemented in a head mounted display device orportable electronic device. In another example, the monolithic waveguidestructure is curved or partially spherical. In another example, two ormore of the DOEs are non-co-planar.

A further example includes a method, comprising: receiving light at anin-coupling region of a diffractive optical element (DOE) disposed in anexit pupil expander; expanding an exit pupil of the received light alonga first coordinate axis in a beam steering and out-coupling region ofthe DOE; expanding the exit pupil along a second coordinate axis in abeam steering and out-coupling region of the DOE; and outputting lightwith an expanded exit pupil relative to the received light at thein-coupling region of the DOE along the first and second coordinate axesusing the beam steering and out-coupling region, in which the beamsteering and out-coupling region includes gratings configured to providea periodic contoured surface having a first periodicity along a firstdirection and a second periodicity along a second direction.

In another example, the periodic contoured surface comprises one ofquadrangular elements, cylindrical elements, polygonal elements,elliptical elements, pyramidal elements, curved elements, orcombinations thereof. In another example, the DOE is formed as a unitaryoptical structure using a polymer that is molded from a substrate thatis etched using ion beam etching in which the substrate has changeableorientation relative to an ion beam source. In another example, thein-coupling region includes gratings configured to provide a periodiccontoured surface having a third periodicity along a third direction anda fourth periodicity along a fourth direction. In another example, themethod is performed in a near eye display system. In another example,the output light provides a virtual display to a user of the near eyedisplay system.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed:
 1. An optical element, comprising: a monolithicsubstrate of optical material forming a waveguide in which one or moreoptical beams are propagated; an in-coupling region integrated into themonolithic substrate, the in-coupling region having an input surface andconfigured with a one dimensional (1D) grating that is periodic in onedirection to couple one or more optical beams incident on the inputsurface into the waveguide; and a beam steering and out-coupling regionintegrated into the monolithic substrate and configured for pupilexpansion of the one or more optical beams along a first direction,wherein the beam steering and out-coupling region is configured with atwo-dimensional (2D) grating that is periodic in two directions, whereinthe 2D grating is configured to provide at least two diverse opticalpaths to each of any given point in the 2D grating for the propagatingoptical beams, wherein differences between lengths of the at least twodiverse optical paths to each of any given point exceed a coherencelength of the propagating optical beams in the beam steering andout-coupling region so as to increase uniformity of output optical beamsand thereby reduce optical interference.
 2. The optical element of claim1 in which the 2D grating includes one of symmetric or asymmetricfeatures.
 3. The optical element of claim 2 in which the asymmetricfeatures include one of slanted gratings or blazed gratings.
 4. Theoptical element of claim 1 in which the beam steering and out-couplingregion includes an output surface and is configured for pupil expansionof the one or more optical beams along a second direction, and furtherconfigured to couple, as an output from the output surface, the one ormore optical beams with expanded pupil relative to the input.
 5. Anelectronic device, comprising: a data processing unit; an optical engineoperatively connected to the data processing unit for receiving imagedata from the data processing unit; an imager operatively connected tothe optical engine to form images based on the image data and togenerate one or more input optical beams incorporating the images; andan exit pupil expander, responsive to the one or more input opticalbeams, comprising a monolithic waveguide structure in which one or moreoptical beams are propagated and on which multiple diffractive opticalelements (DOEs) are integrated, in which the exit pupil expander isconfigured to provide one or more output optical beams, using one ormore of the DOEs, as a near eye virtual display with an expanded exitpupil, and includes an in-coupling region having an input surface andconfigured with a one dimensional (1D) grating that is periodic in onedirection to couple the one or more input optical beams incident on theinput surface into the monolithic waveguide structure, wherein at leastone of the DOEs has a region configured to implement beam steering andout-coupling of the one or more output optical beams from the monolithicwaveguide structure, and wherein at least one of the DOEs includes atwo-dimensional (2D) grating that is periodic in two directions andconfigured to provide at least two diverse optical paths to each of anygiven point in the 2D grating for the propagating one or more opticalbeams, wherein differences between lengths of the at least two diverseoptical paths to each of any given point exceed a coherence length ofthe propagating one or more optical beams in the beam steering andout-coupling region so as to increase uniformity of the one or moreoutput optical beams and thereby reduce optical interference.
 6. Theelectronic device of claim 5 wherein at least one of the DOEs has aregion configured to in-couple the one or more input optical beams intothe monolithic waveguide structure.
 7. The electronic device of claim 5in which the one or more input optical beams received at the exit pupilexpander emanate as a virtual image produced by a micro-display orimager.
 8. The electronic device of claim 5 in which the exit pupilexpander provides pupil expansion in two directions.
 9. The electronicdevice of claim 5 in which the imager includes one of light emittingdiode, liquid crystal on silicon device, organic light emitting diodearray, or micro-electro mechanical system device.
 10. The electronicdevice of claim 5 in which the imager comprises a micro-displayoperating in one of transmission, reflection, or emission.
 11. Theelectronic device of claim 5 as implemented in a head mounted displaydevice or portable electronic device.
 12. The electronic device of claim5 in which the monolithic waveguide structure is curved or partiallyspherical.
 13. The electronic device of claim 5 in which two or more ofthe DOEs are non-co-planar.
 14. A method, comprising: receiving light atan in-coupling region of a diffractive optical element (DOE) disposed inan exit pupil expander formed of a unitary optical structure in whichone or more optical beams are propagated, wherein the in-coupling regionhas an input surface and is configured with a one dimensional (1D)grating that is periodic in one direction to couple the received lightincident on the input surface into the exit pupil expander; expanding anexit pupil of the received light along a first coordinate axis in a beamsteering and out-coupling region of the DOE; expanding the exit pupilalong a second coordinate axis in a beam steering and out-couplingregion of the DOE; and outputting light with an expanded exit pupilrelative to the received light at the in-coupling region of the DOEalong the first and second coordinate axes using the beam steering andout-coupling region, in which the beam steering and out-coupling regionincludes gratings configured to provide a periodic contoured surfacehaving a first periodicity along a first direction and a secondperiodicity along a second direction, and wherein the gratings of theDOE are configured to provide at least two diverse optical paths to eachof any given point in the gratings for the propagating one or moreoptical beams, wherein differences between lengths of the at least twodiverse optical paths to each of any given point exceed a coherencelength of the propagating one or more optical beams in the beam steeringand out-coupling region so as to increase uniformity of output opticalbeams and thereby reduce optical interference.
 15. The method of claim14 in which the periodic contoured surface comprises one of quadrangularelements, cylindrical elements, polygonal elements, elliptical elements,pyramidal elements, curved elements, or combinations thereof.
 16. Themethod of claim 14 in which the DOE is formed as the unitary opticalstructure using a polymer that is molded from a substrate that is etchedusing ion beam etching in which the substrate has changeable orientationrelative to an ion beam source.
 17. The method of claim 14 in which thein-coupling region includes gratings configured to provide a periodiccontoured surface having a third periodicity along a third direction anda fourth periodicity along a fourth direction.
 18. The method of claim14 as performed in a near eye display system.
 19. The method of claim 18in which the output light provides a virtual display to a user of thenear eye display system.